In a conventional image forming device, it is proposed that an image forming system is supported to a frame, and an image forming unit which is a part of the image forming system is detachably mounted on the frame. For example, with regard to a color laser printer having four developing cartridges corresponding to each color of black, yellow, magenta, and cyan, proposal has been made that developing cartridges and photosensitive drums are detachably mounted on a frame as an integral image forming unit. In this case, improved maintenance efficiency can be obtained because four developing cartridges can be integrally removed from a frame.
Japanese laid open patent application publication No. 8-220824 discloses an image forming device in which a door is open when removing and inserting an image forming unit, and movement of the door is interlocked with a support assembly that supports the image forming unit so that the image forming unit is positioned at a prescribed location in the image forming device in response to closure of the door.
However, in the image forming device described above, the image forming unit may be displaced from the prescribed location when the door is open. Accordingly, a lock mechanism is required for maintaining the door in a closed state during image forming operation. However, as described above, the number of parts and components to provide such mechanism increases and configuration of the device becomes more complex if a mechanism for positioning an image forming unit and the above lock mechanism are provided in association with the door.